Electrochemical Evaluation of Light‐Addressable Electrodes Based on TiO₂ for the Integration in Lab‐on‐Chip Systems

Abstract

In lab-on-chip systems, electrodes are important for the manipulation (e.g., cell stimulation, electrolysis) within such systems. An alternative to commonly used electrode structures can be a light-addressable electrode. Here, due to the photoelectric effect, the conducting area can be adjusted by modification of the illumination area which enables a flexible control of the electrode. In this work, titanium dioxide based light-addressable electrodes are fabricated by a sol-gel technique and a spin-coating process, to deposit a thin film on a fluorine-doped tin oxide glass. To characterize the fabricated electrodes, the thickness, and morphological structure are measured by a profilometer and a scanning electron microscope. For the electrochemical behavior, the dark current and the photocurrent are determined for various film thicknesses. For the spatial resolution behavior, the dependency of the photocurrent while changing the area of the illuminated area is studied. Furthermore, the addressing of single fluid compartments in a three-chamber system, which is added to the electrode, is demonstrated.

Photoelectrochemical Imaging System for the Mapping of Cell Surface Charges

“…Recently, electrolyte–semiconductor (ES) structures without an insulator have been shown to be suitable for ac-photocurrent imaging with a good spatial resolution of 2 μm . The ac-photocurrents at these structures feature redox currents, resulting in a photoelectrochemical imaging system (PEIS), which combines the advantages of LAPS imaging by employing a high-resolution LAPS setup developed previously , and recently reported light-addressable electrodes (also named light-activated electrochemistry) (LAE). − LAE have been developed based on different semiconductor materials including monolayers of CdS quantum dots or carbon dots, TiO 2 , , ZnO nanorods, InGaN/GaN nanowires, indium tin oxide (ITO), amorphous silicon, α-Fe 2 O 3 , and silicon protected with self-assembled organic monolayers. , While the organic monolayer limits the potential range silicon can be used in, metal oxide semiconductors such as ITO have the advantage that they can be used at anodic potentials without suffering significant damage, thereby obviating the need for a redox mediator, which could potentially interfere with the cell biology when used for cell imaging applications.…”

3.5 - nduzierte pH-Wert-Änderungen innerhalb mikrofluidischer Kanäle mittels licht-adressierbarer Elektroden

“…Diese Beschichtung wurde gegebenenfalls wiederholt, bis die gewünschte Schichtdicke erreicht wurde. Details zu den Prozessparametern finden sich in [14].…”

“…Die unterschiedlich hergestellten Elektroden wurden anhand der jeweiligen pH-Wert-Änderungen für verschieden angelegte Spannungen miteinander verglichen. Aus früheren Arbeiten geht hervor, dass die Elektroden, welche mittels Sol-Gel und PLD hergestellt wurden, eine TiO2-Schichtdicke von 100-150 nm besitzen und eine ähnliche Oberflächenmorphologie aufweisen, sodass beide LAEs in ihrer Oberflächenbeschaffenheit miteinander vergleichbar sind [14,15]. Die pH-Wert-Differenz der Lösung nach der Beleuchtung mittels LAE kann aus der Änderung der Fluoreszenzintensität berechnet werden, wobei eine pH-Wert-Kalibrierung der Intensität vor der Messung durchgeführt wurde.…”

Light-Addressable Actuator-Sensor Platform for Monitoring and Manipulation of pH Gradients in Microfluidics: A Case Study with the Enzyme Penicillinase

“…To achieve a high spatial resolution of the LAE, a low current in the absence of illumination is required. This can be achieved with a dense and non-porous TiO 2 layer to avoid short circuits with the SnO 2 :F glass [29]. Additionally, it is important to exclude a direct contact of the analyte with the highly-doped SnO 2 :F layer, to circumvent unexpected surface reactions.…”